This invention relates to a cutting tool for the machining of metals in conjunction with the removal of chips and to an arrangement of a tool holder and a cutting bit, the latter being capable of being mounted in a recess in the tool holder and being fastened therein by a clamping jaw, the cutting bit being provided with two cutting edges and with cutting points with the latter being disposed at the end points of a diagonal line.
Complicated shaping of a cutting tool was heretofore required to meet the need of providing for each cutting edge a different recess for the creation of tilted seating planes or surfaces for effecting clamping in such a way that the clamping jaw pulls the cutting bit rearwardly into the seat while being tightened. To avoid such complicated shaping, a cutting tool of the aforesaid kind, according to the present invention, is arranged such that the tilted edges of the frontal planes are formed as auxiliary cutting edges; the cutting bit has a kiteshaped, or preferably a rhombic or a square cross section where the oppositely disposed longitudinal edges serve as the main cutting edges of the cutting tool; a recess is provided in the cutting bit within the area of at least one of the other longitudinal edges, preferably the longitudinal edge which connects the auxiliary cutting edges, the recess being shaped essentially conical or frustro-conical, or forming a seating surface for the clamping jaws in both working positions of the cutting tool, the seating surface being tilted in relation to the seat of the tool holder and also being tilted inwardly upwards. Kite-shaped as used herein means a quadrangle which is formed by two isosceles triangles which are combined at their common bases. When all legs are equal a rhombus occurs, or as a special shape a square.
According to the present invention the provision of the cutting bit with a kite-shaped, or particularly with a rhombic or square cross section, allows an arrangement in such a way that the edges which form the radii of the points are each time disposed diagonally opposite to the other auxiliary cutting edge, so that contrary to the well known two-edge tools, where usually also the auxiliary cutting edges on one hand and the edges of the point radii on the other hand are parallel to each other, two contact planes do not have to be disposed upon the clamping jaw, but the contact planes may abut within the area of an edge and thus may be shaped by a single recess. This leads to a shape of a cutting bit that is made out of a small basic blank, a practice which allows great savings in raw material, particularly in hard alloy, and also allows a simpler method of manufacture and an exact method of clamping.
In a further development of the present invention it may be provided that the direction of the chuck of the clamping jaw and/or its clamping plane which presses unto the cutting tool are tilted against the seat of the tool shaft, at an angle greater than the self-locking action, so that essentially a gripping action results, the gripping action being directed rearwardly into the seat of the cutting tool and essentially in the direction of the diagonal line which connects both cutting points.
This effect may be obtained in a particularly simple manner by shaping the recess as a keyway which traverses the respective longitudinal edge obliquely whereby the recess should preferably end at both sides before reaching the frontal planes in order to secure better mounting and guiding of the cutting bit within the recess of the holder. This improvement includes providing a correspondingly larger abutting plane between the inner seat of the cutting bit, the seat opening each time into the free plane, and the abutting side plane of the recess of the tool holder.
If the recess is essentially conically or frustro-conically shaped, it is possible to develop the present invention by providing two recesses at a distance from each other for two separated fingers of the clamping jaw, such recesses being disposed along a line running obliquely to the longitudinal edge of the cutting bit.
In a further extension of the present invention it may be provided that the frontal planes of the cutting tool are tilted obliquely in relation to the longitudinal side planes in such a way that each time the three edges which form a cutting point form acute angles with each other. This results in a positive cutting bit with a free plane without the provision of a step for guiding the chips which, of course, may be also additionally provided. As a particular advantage the frontal planes should be oriented in such a way that the edge of the cutting tool which embraces the recess forms a right angle with the frontal plane diagonals which extend from its ends. This special choice of the free angle allows a particularly simple fabrication of the cutting bit according to the present invention, because the recess may be formed while the bit is sintered from a hard alloy.
In order to prevent misunderstandings it should be mentioned here that it does not contradict the aim of the present invention when, where according to the present invention, recesses are provided in each of the longitudinal edges of the cutting tool which do not form the main cutting edges of the cutting tool. The contradiction seems to lie in the desire not to provide separate recesses for the clamping jaw for using each of the cutting edges, in other words to clamp the cutting tool in such a way that each time one or the other cutting edge is in an active position. According to the present invention the clamping jaw engages each time the identical recess when the cutting edges are changed. The simultaneous provision of a second recess in the oppositely disposed longitudinal edge has no active function when the cutting tool is used or is clamped. This provision however permits the use of a common blank for the preparation of right or left cutting bits, whereby of course this possibility is restricted to a symmetrical formation of cross sections, in other words a rhombic or square cross section of the cutting tool.
The clamping hold between the cutting bit and the tool holder by aid of a clamping jaw may for example, be provided in such a way that a tapped hole is provided within the tool holder for a setscrew engaging the thread in a bearing leg, the setscrew serving to secure the clamping jaw, a tapped hole being tilted in relation to the accepting borehole in the bearing leg of the clamping jaw. It may be particularly advantageous to provide a spring element between the bearing leg and the bottom of the accepting borehole, the borehole being without an opening at the other end and the spring element being made from rubber. The spring element is compressed when the cutting tool is clamped so that when the clamping is relieved by the relieving of the spring element, the clamping jaw is automatically lifted outwardly, a fact which facilitates removing of the cutting tool, for example, for the changing of working positions.
Finally it is also within the scope of the present invention to build the mounting for the clamping jaw in such a manner that the bearing leg of the clamping jaw has an axially transverse threaded tap which mates with a thread bolt, the bolt being activated when the tool is being activated. The thread bolt is provided at its other end with a thread in an opposite direction for screwing into a tapped hole which follows the accepting borehole for the bearing leg in the tool holder, in which case a hexagonal recess may be provided on both sides of the threaded bolt for a hex-key for the activation of the tool.
This provision prevents the application of two taps which are inclined to each other, one as a bearing recess for the bearing legs of the clamping jaw and one for the setscrew which activates the clamping jaw, a construction which is difficult to provide and which might also detract from the strength of the tool.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.